Automatic telephone system



Nov. 19, 1929. J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM 5 Sheets-Sheet l *Filed July 14, 192'? NNN.

Nov. 19, 1929.

J. E. GARDNER yAUIOMAIIC TELEPHONE SYSTEM Filed July 14, 1927 5 Sheets-Sheet- 2 NNN Ww AUTOMATI C TELEPHONE SYSTEM y Filed July 14, Y192'? 5 Sheets-Sheet 3 wfg@ Nov. 19, 1929. J. E. GARDNER 1,736,283

AUTOMATIC TELEPHONE SYSTEM I Filed July 14, 1927 5 Sheets-sheet 4 Polarized Nov. 19, 1929.

J. E. GARDNER AUTOMATI C TELEPHONE SYSTEM 'Filed July 1'4, 1927 4 5 sheets-sheet 5 i Patented Nov. `19, 1929 i JOHN E. GARDNER, OF CHICAGO, ILLINOIS .AUTOMATIC TELEPHONE BYSTEI Anuman med my 14,

My invention relates in general to ,auto-p matic telephone systems.

One of the objects of the present invention is to provide an improved circuit for con-l trolling the central oice switching mechanism from a subscribers sub-station.

Another object is to provide means for controlling the central ofiice switches by a current or potential balancing arrangement which operates to control theoperation of the switching mechanism in establishing a connection more rapidly .or more positively. Another object is to provide means that is adapted to be temporarily associated with the calling line for bringing the controlling circuit on that line to a predetermined standard so that the controlling. circuit of all calling lines is identical.

Another object is to associate this equalizing equipment with the calling line during the period of controlling the central oiiicel switching mechanism and then to release it and render it available for use by other lines.

Another object is to centralize the mechanism that responds to the control of the calling line which is arranged to control the switching mechanism in establishing a conn ection.

Further objects are to provide new and im- I 3o proved circuits for the connector switches,

selector switches and repeaters.

There areother objects of my invention which, together with the foregom will be described in the detailed specificatlon which is to follow taken in conjunction with the accompanying drawings. .In my copending application, Serial No.

190,397, filed May l1, 1927, a new type of automatic .telephone system is disclosed, 'in which all time functions are eliminated, and in which the operation is speeded so that a connection may be set up in a fraction of 4the time theretofore necessary. The control of the switching mechanism in this prior case depends upon alterin an electrical characteristic of the line whic causes a magnetic balancing circuit, associated with the central oiiice switchin mechanism, to control the setting up of't e connection. AIn the 5 present application this magnetic balancing 1927. lSolial. lo. 805,677.

circuit is employed. c s In the prior application, above mentioned 1t was necessary to have all the lines of the circuit is eliminated and a current balancing V'telephone subscribers in any given exchange of substantially the same resistance. In the present invention it is no longer necessary:n

that every line in a given exchange have the same resistance. No chan e or alteration in the telephone'line is neede While I have shown my invention applied to an automatic telephone stem, it will be obvious that the selecting principle employed is equally applicable to any selecting system such as that employed in telegraphy, supervisory control, train control, and, in fact, in

any selecting system where it is necessary to l control the positioning of a device.

In practicing my invention, I provide a special type of calling device at the subscribers station, as disclosed in thel prior application, above referred to. This calling device is adapted to insert resistance in the line, depending upon the digits dialled -by the calling subscriber. This resistance remains in the line until the dial restores to normal,

when it is withdrawn. The calling device thus alters an electrical characteristic of the line, in this case the conductance. A similar resistance is associated with the central oiiice switching mechanism and an electrical bridge is employed forl balancing one resistance against the other through the movement of the switching mechanism. When the subscriber removes his receiver, the usual automatic trunk selection or line iinding takes place, by which the subscribers line is Vconnected to a first selector. When the first selector trunk is seized, apparatus in the trunk circuit brings about the operation of a finder to select the trunk. The linder has repeating and equalizing equipment associated the circuit at thel sub-station, depending upon vthe digit dialled, and thp conductance of the line is altered. Since the calling line constitutes one leg of the Wheatstonebridge circuit with a controlling relayconnected across the 5 mid-points, the bridge is unbalanced and the controlling rela is energized to imtiate the functioning of t e re eater circuit. Th1s c1rcuit has a small switch associated with it which is automatically. operated to insert re- 10 sistance step-by-step into the fourth leg of the bri ge. When the conductance of the fourth leg of the bridge is .equal to the conductance of the third leg the relay across the mid-points of the bridge is deenerglzed and the operation of the switch ceases. By the operation of the switch a reslstance corresponding to the resistance inserted into the calling line by the callin device is lnserted into the trunkv circuit lea ing to the irst selector. The first selector and the other selecting mechanism is operated by a yWheatstone bridge balancing circuit in a manner similar to that already described. Thus 1t will be seen that the control of the switching devices occur by a current or potential balancing arrangement. This control circuit is, therefore, very accurate and positive.

Since the switching mechanism is operated by a local circuit and arranged so that 1t wlll control the switch as fast as the switching mechanism will operate, the operation of this mechanism takes place at high speed and the connection is established in a fraction of the time necessary in other types of automatic telephone systems. When the connector 1s operated into engagement with the called line, if the line is idle, the common mechamsm which has been associated with the first se'- lector trunk, is released and rendered available for use by another calling line.

While in the drawings the invention has been shown and described as applied to the so-called Strowger type of automatic telehone equipment, it will be understood that 1t may be applied equally well to the so-called panel type, relay type, and, in fact, to all types of automatic telephone systems and Y also toother types of selecting systems.

' Referring nowto the drawings, comprlsing Fi s. 1 to 5, inclusive, suflicient apparatus an circuits have been shownby means of the usual conventional diagrams to enable my invention to be readily explained and understood.

Fig. l shows an automatic sub-statiom-A, which is provided with the usual type, transi `mitter and receiver. The calling device D is of the special type disclosed in my copending application device is adapted to operate the springs 103 and 104.

The line of the sub-station A terminates at'the exchange in a line switch C, and in the.

multiply connected bank contacts of con- -to 342,inc1u's'iv e.

tobe moved vertically by the operation o "vertical nmagnet 306 and are adapted to be above referred to. This callingA insane:

nector switches havin access to the line of the sub-station A. T e line switch C is of the usual rotary t pe having wipers 122 to 124, inclusive eac of whic is adapted to engage a bank of 25 contacts. The wipers are adapted to be rotated step-by-step over their contact bank by the operation of the` stepping magnet 114. The usual type of swltching and line relays 112 and 113 are employed. The line relay 112 is a double wound relay. The line switches such as C have access to a plurality of trunk lines, such as the trunk line comprising conductors 148 to 150, inclusive, extending to the selector S Fig. 3. A trunk circuit G is interposed between the selector S and the line switch 4C in the first selector trunk. This trunk circuit com rises relays 130 to 134, inclusive. The trun circuit Gis ada ted to initiate the operation of a rotary fin er switch such as F which has access to the iirst selector trunks. The mechanical construction of the finder switches, such as F is similar to that of the line switch C, already described.A The finder switches such as F have access to 25 selector trunks. The finders provide suitable trunking arrangement whereby any selector trunk may have an idle finder associated with it or adapted to select it.

An equalizing and repeating circuit J (Fig. 2). is associated with each finder, such as F. This equalizing and repeatin apparatus comprises relays 200 to 20g, inelusive. An equalizing switch 'E is associated with the equipmentv J and is of the same mechanical construction as the line switch C, previously described, and is adapted to be rotated by the operation of the stepping magnet 207. The switch M is a small minor switch having wipers'250 and 251 adapted to engage a series of 11 bank contacts, that is, the wipers stand in engagement with their first bank contacts. This minor switch has an operating magnet 208 and a release magnet 209. The resistances 210 and 211 comprise two legs of the Wheatstone bridge controlling circuit, as will appear.

The irst selectors, such as S shown in Fig. 3, have the usual Strowger type of mechanical construction having a directively controlled vertical movement and an'automatic rotary fitrunk selecting movement. The selector switch is provided with wipers 340 the rotated into engagement with bank contacts, such as 345 to 347 inclusive, the terminals of an idle trunk in the level selected, by a rotary magnet 305. In addition to the usual wipers 340 to 342, inclusive, the selector is provided with a vertical wiper 335. This wiper is adapted to be operated into engagement with the vertical bank contact such as 338. .There is one vertical bank contact for each level 'of These wipers are ada ted the switch, and in addition there is one normal vertical bank contact with which the wiper 335 is in engagement in its normal or released position. The vertical bank contacts are connected to ay resistor 337 that is similaito the resistance 106 at the sub-station A. The vertical bank contacts are conneet-ed to the resistors in such manner that the vertical bank contact standing opposite the first level is connected to the resistor 337 at a point that corresponds to the connection at the second bank contact accessible to the wiper 253 in the minor switch M of the repeating and equalizing apparatus J. This point of connection, may or may not, be the same as the point of the resistor 106 to which the first bank contact of the calling device D is connected. That is, it is not necessary that the vertical bank contacts of the selector switches be connected corresponding to the bank contacts of the calling device at the calling sub-station. All that is necessary is that the manner in which the resistor 337 is connected to the vertical bank contacts 'of the selector switches be the same as the manner in which the resistor 260 is connected to the bank contacts of the minor switch M. The selector switch S is adapted to be released by the operation of the release magnet 307 For controlling the selector switch such as S, relays, such as the relays 300 to 304, inclusive, are provided. Two resistances 308 and 309 constitute two legs of the Wheatstone bridge controlling circuit. A. sensitive relay 300 is bridged or connected midway between or across the bridge. The relay 301 is a quick acting release relay. Relay 302 is an interrupter relay, relay 303 is a switching relay, and relay 304 is a controlling relay.

The trunks accessible to the selector switch S may terminate in second selectors or in connectors, depending upon the size of the system'. It the trunk lines terminate in second selectors and there is more than one exchange in the system, certain of these trunk lines lead to repeaters in order that two wire trunk lines may be used for interconnecting various exchanges.

In the first case, the t-runk lines leading fromthe bank contacts 345 to 347, inclusive, extend by Way of conductors 348 to 350, inclusive, to the repeater R, Fig.'4. The repeater R is provided with relays 400 to 405, inclusive. The relay 404 is an electropolarized relay having an upper polarizing winding and lower low resistance winding for operating the relay.` The operation of the relay 404 is such that it will not attract its armatures until the current flow of both windings is in the same-direction. The relay 405 is a differential control relay. lay 403 is adapted to supply battery to the calling line. The resistances 440 and 441 constitute the two legs of the Wheatstone bridge. The relay 402 is a sensitive relay connected The reacross the Wheatstone bridge. There is a minor switch M1 of the usual construction having the/wipers 433 and 434, each adapted to engage in their rotation in series of ten bank contacts. Each wiper has a normal bank contact with which it is engaged. The minor switch M1 is provided with an operating magnet 406 and a release magnet 407. There is la resistor 435 connected to the various bank contacts accessible to the wiper 433 which serves to providefor variation in resistance in one leg of the Wheatstone bridge control circuit to balance the bridge when there has been a change in resistance in its third leg which includes the controlled circuitextending back to the common repeating and equalizing equipment such as J. The resistorl 435 is connected to the bank contacts accessible to the wipers 433 in a manner similar to which the resistor 337 is connected t-o the vertical bank contacts accessible to the wipers 335 of the selector switch S. Similarly there is a resistor connected to the bank contacts accessible to the wiper 434, so that movement of this wiper may control.the selecting mechanism in the distant exchange in the same manner as if the switching equipment were controlled from a calling telephone through the equalizing and receiving equipment J. The trunk lines comprising the conductors 450 and 451 extending from the repeater R terminate at another exchange in an incoming selector S1. This selector has a circuit that is similar to the selector S, just described and is of the 'usual Strowger vertical and rotary type. The second selector SL has access to the trunk lines leading to third selectors or to connectors depending upon the size of the system. Since third selectors have the same circuit as the first selector S it will be assumed that the trunk line comprising conductors 470 and 472, inclusive, extend to connector switches such as H.

The connector switches, such as H, are of the usual Strowger vertical and rotary type. The connector H is provided with vertical and rotary magnets 509 and 510 and a release magnet 508. The vertical and rotary magnets are adapted to operate the Wipers 555 to v558, inclusive, first in a vertical and then in a rotary direction. Connector switches H are also provided with vertical wipers such as 560. These wipers are adapted to engage a vertical bank of 10 contacts. In addition, all the connector switches have an extra wiper, such as the wiper 557 for. controlling the rotary movement of these switches. This wiper and associated bank .contacts are identically the same as those employed and so-called rotary connectors manufactured by the Automatic Electric Company of Chicago. A resistor such as 554, is connected to the vertical bank contacts in the manner shown, and to the rotary bank contacts, corresponding rotary contacts in to be supplied the various levels being connected together.' The connector switch H is provided with rela s such as 500 to 507, inclusive, of the usual te ephone type. The resistances 511 and 512 are associa-ted with connector switch H and constitute two legs of the Wheatstone bridge circuit. The relay 500 is connected across the mid-portion ot the bridge. The relay 501 is adapted to supply talking battery to the calling line. Relay' 502 is what is known as a two-step or counting relay. When the upper winding of the relay 502 is energized only the armatures 521 and 526 are operated, but when the upper and lower windings ot' the relay 502 are energized all the armatures of this relay are attracted. Thel relay 503 is an interrupter relay. The relay 504 is the usual type of cut-ott relay. The relay 505 is a back bridge relay for supplying talking battery to the called line. Thev relay 506 is a busy control relay. The relay 507 is a switching or cut-in relay.

The connector switch H has access to called subscribers line, such as the line of the substation A1, for the bank contacts 565 to 568, inclusive. The sub-station A1 is similar to the sub-station A previously described. The line switch C1 is the called subscribers line switch and is similar to the line switch C previously described. The calling subscriber is ada ted with a busy tone from the usy machine BB in the event that the call line is busy, whil-e the called sub-station is rung intermittently by ringing current from the ringing equipment R1. These devices are of the usual type and need not be described in detail. Y

`While in the drawings positive -land negative signs have been used to indicate the battery connection, which may or may not be connected to ground, while indicates the usual negative battery connection. common battery is employed for each exchange. A booster battery may be connected in series with the main battery for the control of the common equalizing and repeating equipment such as J of Fig. 2 in the event that onel is needed or desired. This connection is-totally unnecessary in connection with any of the other switching mechanisms, as will appear more fully hereinafter.

Referring now to the drawings, a detail description of the operation of my improved telephone system will be given. For this purpose, it will be assumed that the subscriber at sub-station A desires to call the subscriber at sub-station A1. In order to accomplish this result he will remove his receiver from the switch hook and operate his calling device D in accordance with the digits of the called subscribers number. When the receiver is removed at sub-station A there is a circuit completed that extends from ground by way of back contact and armature 118, line conductor 110, transmitter 105 of sub-station A,

springs 103, switch hook springs, line conductor 111, armature 115 and its back Contact and upper winding of line relay 113 to battery. The line relay 113 is energized over this circuit and operates to complete a circuit at armature 120 over a path that extends from ground through the lower winding of relay 113, armature 120 and its front contact switching relay 112, back contact and armature 117, and motor magnet 114 to battery. l Another result of the operation of the relay- 113 is that at armature 119 there is a circuit completed that extends from the wiper 123 by way of armature 116 and its back contact, front contact and armature 1.19 to a point midway between the switching relay and the stepping magnet in the previous] traced circuit. If the trunk line with whic the wipers 122 to 124,-inclusive, of the line switch C are in engagement is idle, the switching relay 112 is immediately energized in series with the motor magnet 114. Because the relay 112 is'of relatively high resistance with respect to the motor magnet 114, the latter is not operated over this circuit. In theevent that the lwipers 122 to 124, inclusive, of the line switch C are not in engagement with the bank contacts of an idle trunk, there will be a ground potential present upon the bank contact that is engaged by the test wiper 123 and the relay 112 will be short circuited and the motor magnet 114 will operate as a buzzer to advance the,-

lswitch C. When the switch wipers are rotated into engagement with these bank contacts, the relay 112 will be energized over the circuit previously traced. The relay 112 A upon operating, opensy a point in the circuit the motor magnet 114 on armature 116, places ground upon the bank contact 126 at the front contact of this'armature, opens the circuit of the upper winding of the relay 113 on armatures 115 and 118, and at the front contact of these armatures extends a calling line to the trun circuit G. It will be noted that as soon as t e line relay is energized that ground is connected to the private normal conductor 121 that is multiply connected in the banks of the connector switches so as to busy the line of the sub-station A with respect to these switches. The grounding of the bank contact 126 occurs overa circuit that eX- tends from ground through the lower winding ofthe line relay 113, armature 120 and its front contact, front contact and armature 116, test wiper 123, bank contact 126, normally closed springs controlled by armature 143, armature 141 and its back contact, and relay 130 Vto battery. The connecting of this ground to the test contact 126 renders the selected trunk line busy, so that it is not accessible to the other line switches such as C through its multiples. The line relay 113 reniains energized for the present maintaining its own circuit and that of the relay 112 as well as the circuit ot' the relay 130 in the trunk circuit (i. 4 The relay 130 in the trunk circuit G, upon operating prepares a locking circuit for itself and armature 135, removes ground from the bank contacts such as the bank contact 167, in the banks ot' finder switches F which have access to the first selector trunk such as G.

Another result of the operation of the relay 130 is that at armature 137 a circuit is prepared for the relay 133. A further result of the operation ofthe relay 130 is that at armature 136 there is a circuit completed which extends from ground by way of armature 145 and its bank contact, armature 136 and its front contact to starter wire 172, to start an idle nder. It will be assumed that the inder switch F is the first idle finder and in this event there will be a circuit completed for the upper winding of the relay 151. The relay 151 is energized over this circuit to complete a circuit on armature 154 that extends from ground through its lower winding, by Way of said armature and its front contact, switching rela)-v 152, back contact and armature 179, and motor magnet 180 to battery. Another result of the operation of the relay 151 is that at armature y153 a short circuit is completed to shunt the relay 152. This short circuit extends to the test wiper 152 of the finder switch F. Since the first selector trunks accessible to the finder switch F have ground connected to all their test contacts except when the first selector trunk is seized, the bank contact 157 is the only one from which ground is removed by the operation of the relay such as 130. A circuit is thereby completed for the motor magnet 180, and this magnet operates as a buzzer to advance the switch wipers 162 to 166, inclusive, step-by-step until these switch wipers are brought into engagement with the bank contacts with which the trunk circuit G is connected which, in this instance is the bank contacts 167 to 171, inclusive. When the potential present upon the bank contact 167,

I 'there is no circuit for the rotary magnet 180 and the switching relay 152 is energized in series with the motor magnet. The motor ,magnet is not operated over this circuit by 4 reason of the relatively high resistance of the relay 152. The relay 152 upon energizing,

Vprepares a locking circuit for itself at armature 156, connects ground to the test 'Wiperv V162 lat armature 158, at armatures 157 and 159 extend the 'conductors of the calling line 'uso as to complete a circuit for the relay 205 in the common equalizing and repeating connects the first selector S under the control of the repeating equipment J.

The connecting of ground to the test wiper `162 brings about the completion of a circuit which extends from ground by way of armature 294 and its back contact in the common equalizing and controlling equipment J, conductor 181, front contact and armature 158, test wiper 162, bank contact 167, front contact and armature 137 in the trunk circuit G, and relay 133 .to battery. The relay 133, upon operating, completes the circuit at armature 144 or the relay 131, removes ground from ,the starting circuit at armature 145, completes a locking circuit for the relay 130 at the front contact of this armature, and at armature 143 opens the original energizing circuit of the relay 130 and connects direct ground to the release trunk conductor. .The connection of ground to the release trunk conductor establishes a holding circuit for the switching relay 112 in the line switch C over a path that extends from ground by Way of armature 147 and its back contact, front contact and armature 143, release trunk conductors, back contacts 126, wipers 123, armature 116 and its front contact, relay 112, back contact and armature 117, and stepping magnet 114 to battery. This circuit serves to short circuit the lower winding of the line-'relay 113. The line relay 113 is thereupon deenergized to open a point in the selector circuit on armature 120 and to open a point in the' stepping circuit in the magnet 114 on armature 119.l

As mentionedl before, the operation of the armature 145 and the relay 133 serves toremove ground from the starting Wire 172 which is extended to the next finder by the operation of the armature 155 of the relay 152 in the finder switch F. The relay 152 at armature 155 also opens the circuit of the upper Winding of the line relay 151, but this relay is maintained energized to prevent the relay 152 from deenergizing over a circuit that includes its lower winding.

The relay 205 in the common repeating equipment J is energized over a circuit that extends from ground by way of the normally closed springs controlled by armature 215, relay 205, normally closed springs controlled by armature 216, conductor 174, armature 157 and its front contact, wipern163, bank contact 168, normally closed springs controlled by armature 183, bank contact 127, wiper 124, front contact and armature 118, over the conductors ofthe calling line loop, armature 115 and its back contact, Wiper 122, bank Contact 125, normally closed springs controlled by armature 139, bank contact 169, Wiper 164, armature 159 and its front contact, conductor 175, and normally closed springs controlled by armature 230 to battery.

The release relay 205 is energized over the above circuit, and, upon operating, completes a circuit for the relay 205 and armature 228,

completes a circuit for the lower winding of the relay 206, removes from the multiply con- 'battery to the Wheatstone bridge control circuit and at the front contact of the armature 230 connects direct battery to the mid-point between the resistors 210 and 211 of the Wheatstone bridge control circuit. The circuit for the relay 205 extends throu h the resistor 210 and armature 230 and its ront con- 2'0 tact to battery. The resistors 210 and 211 comprise two legs of the Wheatstone bridge. The third leg comprises the subscribers line circuit including the relay 205. The fourth leg of the Wheatstone bridge extends from the junction 266 of the resistor 211, wiper 242, bank cont-act with which said wiper is in engagement, resistor 269, normally closed.

springs controlled by armature 221, to ground by way of front contact and armature 229. In order that the bridge may be balanced it is necessary that the conductance of 'a circuit including the calling subscribers line loop be vproportional to conductance including the wipers 242 and its associated bank contacts. The value of the proportion is controlled by the proportion of the resistors 210 and 211 of the first and second leg ofthe bridge. In order to simplify the description, it will be assumed that the resistances 210 and 211 are exactly equal. It will, therefore, be neces sary that thev resistances of the third and fourth leg of the bridge be exactly equal in order that the bridge be balanced. The resistor 269 is included in the circuit of the fourth leg of the bridge to compensate for the resistance of the winding of relay 205.

It will be seen that the relay 204 is connected across the bridgebetween the points 266 and 267. This relay takes the place of the ordinary galvanometer employed in Wheatstone` bridge circuits. This relay is quite sensitive and serves to control the operation of the equalizing` and repeating equipment. l The sensitivity of this relay depends upon the voltage of the battery connected across the Wheatstone bridge control circuit and upon the change in conductance in the third leg of the bridge brought about for each successive setting of the calling device. If these changes in conductance are relatively large a relay of less sensitivity may be employed. The numberof ampere turns and the adjustment of this relay can be very easily ascertained from calculating the lchanges in conductance in the third leg of the bridge and the amount of current flow through it. That is, it is necessary that this relay remain ener. gized until the third and fourth legs of the ridge are balanced and to then deenergize. Since the telephone lines coming into the central ofce are of dierent lengths and sometime different characters, their conductance varies over a considerablerange. Now, since the calling devices at the sub-stations are designed to alter the conductance of the lines a predetermined lamount in order to control the central oice switching mechanism, in order to avoid connecting the bank contacts of the calling device to their associated resistors differently on each telephone line, it is necessary to provide some means for making the conductance of all telephone lines substantially equal. In my prior application the method employed was to introduce a resistance in the line of each subscriber atthe telephone exchange toy bring his line up to a predetermined standard. In the present case the line equalizing and repeating equipment J "is adapted to accomplish this result.

When the subscribers line is connected to the Wheatstone bridge control circuit it has a certain amount of resistance, while( the fourth leg of the bridge has very little resistance except the resistance 269, which compensates for the resistance of thelwinding of the relay 205. The bridge is, therefore, unbalanced and the relay 204 is energized. The result of the operation of this relay will be discussed shortly.

A resistor 270 is connected to the various bank contacts accessible to the wiper 242, which are 25 in number. The value of this resistor ,is equal to the resistance ofthe long.- est line coming into the exchange. A similar resistor 271 is connected to the bank contacts accessible to the Wiper 243. It will be seen that any movement of the wiper 242 serves to introduce resistance into the fourth leg of the bridge. The movement of the wiper 243 serves to introduce a resistance into the third leg of the bridge including the calling subscribers line loop after the balancing operation has been performed.

The operation of the relay 204 serves to open a point in the releasing circuit ofthe equalizing switch E at armature 227 and to complete a circuit at the front contact of this armature forthe interrupter relay 203. Another result ofthe operation of the relay 204 is that the original circuit of the lower winding of the relay 206 is opened. Vhen the circuit'of the relay 206 is completed by the energization of the relay 205, the relay 206 merely attracts its armature 234, the other armatures 233 and 235 of the relay remaining inoperative until both the upper and lower windings of the relay 206 arc energized in series. This occurs when the relay 204 is energized as described. By theoperation of the relay 206 a circuit is prei pared for the relay 207 at amature 233 and a circuit is completed at armature 235 which extends from ground by way of armature 224 and its front contact, front contact and armature 235, armature 213 andV its back contact, armature 239 and its back contact, armature 272 and its back contact, and relay 203 to battery.

The relay 201 is energized over a circuit that extends from ground by Way of relay 301 in the first selector S, normally closed springs controlled by armature 327, trunk conductor 150, back contact and armature 182, bank contacts 171, Wiper 166, armature 161 and its front contact, conductor 178, bank contact 253 of minor switch M, Wiper 251, armature 231 and its front contact, lower Winding of electropolarized relay 202, upper Winding of relay 201, conductor 177, front contact and armature 160, Wiper 165, bank Ycontact 170, armature 140 and its back contact, trunk conductor 148, normally closed springs controlled by armature 322, and resistor 308 to battery. The relay 301 is energized over this circuit and, upon operating,

connects ground to the release trunk conductor 149 at armature 312 over a path that extends from ground by Way of armature 329 and its back contact, back contact, back contact and armature 323, oil' normal spring 317 and its resting contact, front contact and armature 312 to release trunk conductor 149, completes a circuit for the relay 302 at armature 313 over a path that extends from ground by Way of armature 329 and its back contact, back contact and armature 323, armature 313 and its front contact, backcontact and armature 328, back contact and armature 334, armature 333 and its back contact, and relay 302 to battery; opens a point in the release magnet circuit at armature 315 and at the front contact of this armature connects ground to the vertical Wipers 335.

The circuit for the relay 301 including the trunk conductors 148 and 150 constitutesa third leg of the Wheatstone bridge control circuit. The fourth leg may be traced from the ground and vertical Wipers 335, resistance 336 to the point 360 of the resistance 309. In order that the bridge be balanced, it is necessary that theresistance of the third leg equal the resistance of the fourth leg of the bridge. The resistance 336 in this circuit is a fixed resistance designed to compensate tor the resistance of the trunk loop and for the resistance of the relay 301. The relay 300 is bridged across the Wheatstone bridge and constitutes the controlling means for the selector switch S. Since, the minor switch M in its normal position, the third and fourth legs of the bridge are in balance and the relay 300 is deenergized. The relay 302 is operated to open a point in the ground connection to the release trunk at armature 319, to establish a locking circuit for itself at the relay 201.

armature 320, and to complete a point in the circuit of the vertical magnet 306 at armature 321.

The connection of ground to the release trunk conductor 149 brings about the enerzation of the relay 134 in the trunk circuit l The relay 134 is operated to extend the release trunk conductor 149 to the bank contacts 126 and armature 146 and to remove the ground connection through armature 147 in the trunk circuit G. In the common repeating equipment J the relay 201 isenergized in series with the relay 301 of the selector switch Sp The lovver Winding of this relay has no effect on its operation at present time as its circuit is open. The relay 201 is energized to open one pomt in the release circuit of the minor switch M at armature 237 and to establish a locking circuit for the relay 206. The electropolarized relay 202 has its lower Winding in series with the upper Win'ding of The relay 202 is not energized because the current flow in its two windings is in opposite directions.y The relay 203 is energized to establish a locking circuit for itself at armature 224 and to complete a circuit at armature 225 that extends rom ground by Way of armature 229 and its front contact, armature 223 and its back contact, armature 225 and its front contact, armature 220 and its back contact, and stepping magnet 285 and the line equalizing switch E to battery. The stepping magnet 285 operates to position its paWl and to open the locking circuit of the relay 203. The relay 203 is deenergized to open a circuit of the stepping magnet 285. The stepping magnet 285 is deenergized to advance the Wipers 240 to 243, inclusive, one step into engagement With their second set of bank contacts and to 'complete a circuit for the relay 203 at armature 272. The relay 203 and the stepping magnet 285 are alternately operated so long as the relay 203 remains energized. The operation of the Wiper 242 into engagement with the second bank contact introduces a certain amount of resistance into the fourth leg of the Wheatstone bridge. The step-bystep movement of this Wiper thus brings about the balancing of the bridge. That is, when the Wiper 242 has introduced an amount of resistance Which alters the conductivity of the fourth leg of the bridge so that the conductivity thereof is equal to the conductivity of the third leg, which includes the calling subscribers line loop there will be no current l'low through the control relay 204 and this relay Will be deenergized. vWhen the relay 204 retracts its armature 227 the circuit of the interrupter relay 203 is opened and this latter relay remains deenergized to open the circuit of the stepping magnet 285. A further result of the deenergization of the relay 204 is that at armature 227 there is a circuit completed that extends from ground by way of said armature and its back contact, bank contact with which the wiper 240 is in engagement, and said wiper, normally closed springs controlled by armature 217, and relay 200 to battery. The relay 200, upon operating, establishes a locking circuit for itself at armature 217 connects dial tone to the calling line at armature 215, introduces -a resistance to alter the conductivity of the calling loop control circuit at armature 216, cuts the resistance 212 into the circuit of the fourth leg of the bridge at armature 219, opens a point in the circuit of the stepping magnet 285 at armature 220, completes a point in the circuit of the stepping magnet 208 at the front contact of -this armature and at 'armature 221, places the fourth leg of the Wheatstone bridge under the control of the minor switch M, as will appear. The movement of the wiper 243 serves to measure sutiicient resistance to be inserted in the calling line to bring it up to a standard resistance.

The resistance 212 is a fixed resistance that is adapted tobe inserted into the third leg of the bridge. This resistance has a value equal to the resistance value of the longest line in the exchange. The calling line loop is connected through the resistor 270 to the 25th bank contact accessible to the wiper 243. It will be seen that if the calling line loop is of relatively low resistance, the wiper 242 will only take a few steps, as by this movement it will have balanced the bridge. Since the resistance of the line is small it is necessary to insert a greater amount of resistance into this line than it would be if the resistance of the line was greater. This is accomplished by the connection ofthe calling line loop to the 25th bank contact, thus if the vwiper 243 is moved only a few steps a greater amount of resistance will be inserted into the calling line upon the energization of the relay 200. In this manner the resistance of all the calling lines are brought up to a predetermined standard. Since, the fourth leg of the bridge has a fixed resistance inserted into it which balances the resistance of the calling line, the resistance of the line can be disregarded and the operation of the calling device E at the calling sub-station will bring about the same alteration of conductance in the calling line circuit on each and every line. If de'- sirable, a booster battery may be insertedin this control circuit which includes the Wheatstone bridge and the relays 204 of a common repeating equipment.y It is only necessary to insert this booster battery,'if one is used, in

the common equalizing and controlling equipment J.

Since the calling device D on the various telephone lines brings about the same alteration in conductance of the line for a given digit the controlling relays such as 204 in thel various repeating and equalizing equipments need no maroinal adjustment, as is the usual practice. That is, in the present type of automatic telephone system working on the two Wire principle, it is necessary to margin the line relay to work under varying line conditions and this is taken care of by margining the relay so that it will work between certain limits. This is done in addition to the various time margin adjustments that have to be given to the various relays ``with the attendant diculties which have been explained in my prior copending application,\above referred to.

Referring now to the operation of the common equalizing and repeating equipment J. After the relay 200 is energized, the circuit of the fourth leg of the bridge can be traced from the point 266 of the resistor 211, front contact .and armature 219, fixed resistor 212, bank contact 252, wiper 250, armature 221 and its front contact, to ground lupon trunk conductor 265. Since the resistance of the calling line is balanced by the resistance 212 the relay 204 remains deenergized. By the connection of dial tone from the dial tone inachine D. T. to the calling line a signal is given to the calling subscriber that he may now operate his calling device in accordance `with the digits of the called subscribers numer. e,

When the calling device D at.v sub-station A is operated in accordance with the first digit of the called subscribers number, the wiper 100 of this calling device is positioned into engagement with a certain bank contact. When this positioning occurs the springs 104 are closed and the springs 103 are opened. In this manner the circuit of the transmitter and receiver is opened and a certain amount of resistance is placed in the calling loop circuit depending upon the position of the wiper 100. The resistance 101 serves to compensate for the resistance of the transmitter and receiver. In this manner the conductance of the calling loop circuit is altered in predetermined amount. This alteration in the conductance of the calling loop circuit, which is a third leg of the bridge unbalances the bridge and unbalances the bridge and brings about the energization of the relay 204 in the common repeating equipment J.

The relay 204 upon operating opens the original energizing circuit of the relay 200 at armature 227 and at the front contact of this armaturecompletes a circuit which extends from ground by way of said armature and its front contact, front contact and armature 235, armature 213 and its back contact, armature 239 and its back contact, armature 272 and its back contact, and relay 203 to battery. This circuit is completedbecause the relay 206 is completely operated by the movement of the armature 227, removing the short circuit from the upper winding of the relay 206. The relay203 is operated to establish I a locking circuit for itself on armature 224 and to complete a circuit at armature 225 that 4e\tends from ground upon grounded conductor 265, armature 223 and its back contact, armature 225 and its front contact, armature 220 and its front contact, and stepping magnet 208 of minor switch M to battery. The stepping magnet 208 of' the minor switch M is energized to advance the switch wipers 250 -and 251 one step into engagement with their first oil' normal set of bank contacts or their second set of bank contacts and to open the circuit of the relay 203 at armature 239. lhe relay 203 is deenergizcd to open its locking circuit at armature 224 and to open the circuit of the stepping magnet 208 at armature 225. The stepping magnet 208 is deenergized to position its pawl and to complete a circuit for the relay 203 at armature 239.4

'lhe 'movement of the wiper 250 serves to introduce a certain amount of resistance in the fourth leg of the Whcatstone bridge. The amount of resistance introduced corresponds to the amount introduced in the third leg when the wiper 100 of the calling device E is positioned in engagement with the irst bank contact. The alternate operation of the relay 203 and the stepping magnet 208 continues until the. switch wipers 250 and 251 are advanced sufiiciently so that the wiper 250 has introduced an amount of resistance in the fourth leg of the bridge, so that the conductance of the fourth leg of the bridge equals the conductance of the third leg which includes the calling subscribers loop and the resistance inserted by the calling device D.

'Ihe movement of the wiper 251 of the minor switch M brings about an alteration in the conductivity of the controlling circuit of the selector S, the circuit of the third leg of the Wheatstone bridge of the selector S having been traced through the wiper 251 of the minor switch M.

When the wiper 250 of the miner switch M has introduced the proper amount of resistance into the circuit of the fourth leg of the bridge the wipers 250 and 251 of this switch are in a position corresponding to the position of the wiper 100 in the calling device D and the control relay 204 is deenergized to open the circuit of the relay 203 so that the movement of the switch wipers 250 and 251 ceases.

In the selector S, the conductance of the third leg of the bridge controlling this sclector having been altered by the operation of the wiper 251 of the minor switch M the relay 300 is energized. Upon operating, the relay 300 completes another point in the circuit for placing ground upon the release trunk conductor 149 exclusive of the ofi normal spring 317 at armature 310, opens a point in the circuit of the rotary magnet 305 at armature 311 and at the front contact of this from ground by way of said armature and its front contact, vertical magnet 306 and armature 321 and its front contact to battery.

The vertical magnet 306 is operated to raise the switch shaft carrying the switch wipers 340 to 342, inclusive, opposite the first level of bank contacts and to open the locking circuit and energizing circuit of the interrupter relay 302'` at armature 334. The interrupter relay 302 is deenergized to open theA circuit of the vertical magnet. at armature 321 and to open its locking circuit at armature 320. The vertical magnet 306 is deencrgized to position its pawl and to complete a circuit for the interrupter relay 302 at armature 334. Upon the first off normal step of the switch shaft the off normal springs 316 to 318, inclusive are shifted. By the operation of the spring 316 a circuit is prepared for the release magnet 307. The operation of the vspring 318 servesto prepare a circuit for the switching relay 303 while the operation of the spring 317 opens the original circuit that supplies ground to the release trunk conductor 149. However, this last operation has no effect in View of the fact that ground is supplied to the release trunk conductor 149 by way of armature 310 and its front contact. magnet the vertical wiper 335 is brought into engagement with its second bank contact. This operation serves to introduce a certain amount of resistance into the circuit of the fourth leg of the bridge. Unless this resistance is equal to the resistance inserted into the third leg of the bridge by the operation of the wiper 251 of the minor switch M, the bridge remains unbalanced and the relay 300 remains energized.

The circuit for the interrupter relay 302 By the operation of the vertical the interrupter relay 302. The operation of the interrupter relay 302 and the vertical magnet 306 continues until the switch shaft carrying the switch wipers 340 to 342, inclusive, are brought into engagement with the proper lever of bank contacts. At this point l the vertical wiper 335 will have introduced an amount of resistance into the fourth leg of the bridge corresponding to ther resistance in the third leg of the bridge inserted by the operation ofthe wiper 252 of the minor switch S and the third and fourth leg of the bridge` will be balanced. The relay 300 is thereupon deenergized to open the vertical magnet circuit at armature 311 and to prepare the rotary magnet circuit at the back contact of this armature. A further result of the operation of the relay 300 is that the'direct ground connection through the armature 310 to the release trunk conductor 149 is open. vHowever, ground is still connected to the release trunk conductor over a circuit that extends from ground by way of armature 329 and its back contact, back Contact and armature 323, back contact and armature 319, front contact and armature 312 to the release trunk conductor 149. However', the original circuit for the interrupter relay 302 is still maintained so that this relay is energized to establish a locking circuit for itself on armature 320 and to remove the direct ground connection previously traced from the releasetrunk corductor 149. This operation removes the short circuit from the relay 304 which now serves .to supply ground to the release trunk conductor 149 over a circuit which extends from ground by Way of armature 315 and its front contact, relay armature 312 to'release trunk conductor 149. This circuit serves to maintain the relay 134 in the trunk circuit and the switching relay 112 in the line switch C energized, as well as to busy the first selector trunk, the relay 304 being of relatively low resistance. The relay 304, upon. energizing opens a point in the original energizing circuit ofthe interrupter relay 302 at armatures 328 and 329, establishes a new circuit for itself at armature 330 exclusive of the front contact and armature 312 of the relay 301, prepares` a-point in the circuit of a. relay such as 403 if the trunk lines in the level selected lead to repeaters or prepares a point in the circuit of a relay, such as 301 in the next selector, and at armature 331 completes a circuit of therrotary magnet 305. The rotary magnet 305 is energized to open the circuit of the interrupter relay 302'at armature 333 and to advance the switch Wipers 340 to 342, inclusive, into engagement with the first set of contacts in the selected level.

If this trunk line is idle the switching relay 303 is energized to connect the trunk conductors 148 and 150 to the trunk conductors extending to the next switch. However, if this trunk line is busy there will be a ground potential upon the bank contacts engaged by' the test wiper 341, and there will be a circuit completed that extends from this groundby way of switch Wiper 341, armature 324 and its' back contact, back contact and armature 334, armature 333 and its back contact, and interrupter relay 302 to battery. This circuit serves to short circuit the switching relay 303 so thatv it remains deenergized. The relay 302 is operatedy to establish a locking circuit for itself at armature 320 and to complete a circuit for the rotary magnet 305 at armature 321. The rotary magnet 305 is en- 304, front contact and v 1,7es,2ss n ergized to advance the switch wipersA another step and to open the circuit of the interrupter relay 302, which is deenergized to o en the circuit oi the rotary magnet. The a ternate operation ofthe relay 302 and the rotary magnet 305 continues until the switch wipers 340 to 342, inclusive, are brought into-engagement with the bank contacts associated With an idle trunk, which, in the present case, it will be assumed are the bank contacts 345 to 347, inclusive, to which the trunk lines comprising conductors 348 to 350, inclusive, are connected. lVhcn the switch wipers are brought into engagement with this setV of bank contacts there will be no ground potential present upon the bank contact 346 engaged by the test wiper 341 and there will be no circuit completed lfor the interrupter relay 302. The relay 303 is thereupon energized over a circuit which extends from ground upon release -trunk conductor 149 working contact of of:1 normal spring 318 and said spring, relay 303, back contact and armature 334, armature 333 audits back contact and relay 302 to battery. The relay 303 is energized over this circuit to establish an alternative circuit for the relay 304 which supplies ground to the release trunk at armature 325. The relay 302 is not energized in series with the relay 303 because of the relatively high resistance of the relay 303. Other results of the operation of the relay 303 are that at armatures 322 and 327 the control circuit including the Vheatstone bridge and the relay 301 is opened vand the trunk conductors 148 and 150 are extended to the trunk conductors 348 and 350, a point in the circuit of the release magnet-is opened at armature 326 and battery is connected to Wiper 342 at the front Contact of this armature, and at armature 323 a point in the original energizing circuit of the relay 302 is opened. The relay 301 is deenergized to open the original energizing circuit of the relay 304 at armature 315, to complete a point 1n the circuit of the release magnet 307 at the back contact of this armature, and to open a point in the original circuit by which ground is connected to the release trunk at armature 312. A further result of the operation of relay 303 is that ground is connected to the wiper 340 through .the resistor 352, front contact and armature 339, armature 351 and its front contact to wiper 340. This circuit is to momentarily maintain the control circuit of the next switch inoperative until the relay 304 is deenergized. The resistor 352 4is to compensate for the resistance of the control loop which is not included in the control circuit for the present. When the battery is connected to the Wiper 342v there is a circuit completed that extends by Way of this wiper, bank contact 347, trunk conductor 350,

normally closed springs controlled. by armaspring '43() and said spring to ground. The relay 403 viii the repeater R is energized over this circuit to connect direct ground to the release trunk conductor 349 at armature 420 ing. -lhis speed may be four or tive times to establish a bridge across the trunk condiictor 450 and 451 at armature 422, to establish a point iii its locking circuit through its lower winding at ariiia'ture 423, and to open a point iii the circuit ot the release magnet 407 at ariiiature 424,

lVhen the relay 303 in the selector S is energized the operation of the armature 327 does not extend the trunk coiidiictois 150 to the 'trunk conductor 350 until the relay 304 is deenergized. Consequently, the control cii'- cuit which constitutes the third leg of the Vheatstone bridge is opened momentarily. This operation brings about the opening ot the circuit of the upper winding of the relay 3 201 inthe coiiinion repeating equipment J. The relay 201 is deenergized to open the locking circuit of the relay 206 at armature 237 to establish a circuit tor the release magnet 209 at the back contact of this armature over 5 a path that extends from ground upon grounded conductor 265, armature 237 and its back contact, and release magnet 209 to battery, and to establish a circuit for its lower winding at armature 236 over a ath that extends from ground by way ot ack contact aud aiii'iature 226, ofi1 normal spring 23S and its working contact, back contact and armature 36, and the lower winding of relay 201 tofbatteiy. This is the differential winding 3 of the relay and while it is not sufficiently powerful to operate t-lie relay armature, it seri-es to maint-ain the relay deenergized eijcn though the circuit Jfor its upper winding is closed.A The release magnet 209 operates to. bring-about release o't the wipers 250 and 251 ot the minor switch M to their normal positions. By the movement of the wipers 250 to its noi'ii'ial position, a change is made in the conductance of the fourth leg of the bridge and the control relay 204 is again energized. However, the operation of the relay 204 is without 'function at this time by reason of the tact that the deenergization at the relay 201 brought about the deenergization of the relay y 206 to open the circuit ot the interrupter relay 203. The relay 206 is deenei'gized to open a point in the circuit of the interrupter relay 203 at armature 235 to open its locking circuit at armature 234 and to prepare a circuit t'or its lower winding at armature 233. A restoration ot the wiper 251 of the minor switch M removes the resistance from the bridge across the trunk conductors 148 and 150 extending to the repeater R so that the third and fourth leg of the `Wheatstone bridge circuit controlling the opei'ation of the repeater R are balanced, and the minor switch M having beenl released as described, the relay 402 remains deenergized.'

Since the switching devices such as the selector switch in the central otiice operate under a local interrupter circuit they will oiperate at a very high speed as compared with tie usual directive control through impulsas fast as the usual directive control speed. The calling device dial can thus be permitted to return to normal very rapidly. This has been explained in the copending application referred to hereintofore. It may sometimes occur that the calling device dial returns to normal a great deal more rapidl than it is adjusted for, oi', that a selecting dlevice in the exchange by reason of mechanical trouble or poor adjustment will not be through operating by the time the dial restores to normal. Under these conditions unless some provision were made a wrong number will be secured. In order to obviate the possibility of this I provide means associated with the common line equalizing and repeating equipment such as J for maintaining the control circuit to tlie switch to which the connection has been extended locked up until the switch is operated. This gives considerable additional time dui-ino the pause between the separate digits dialer by the -calling subscriber and until the next digit has been set up, for v the equipment to operate. This provision automatically rotects the system against abnormal conditions such as are introduced by faulty dial construction or adjustment or faulty switch construction .or adjustment. This provision will now be described.

It will be assumed that the switch wipers 250 and 251 of the minor switch M are in their operated position and that the selector switch S has not yet selected an idle trunk for one of the reasons mentioned when the calling device dial B at the substation A restores to normal, thereby altering the conductance of the third leg of the bridge, extending to the common repeating equipment J. The positioningI of the wiper 250 and the deenergization of the relay 204 bring about the completion of a circuit that extends from ground by Way of armature 227 and its back contact, armature 228 and its front contact, armature 233 and its front contact, and relay 207 to battery. The relay 207 is energized to establish a locking circuit for itself at armature 212 to ground through the oit normal spring 297 and to open the circuit ofthe interrupter relay 203 at armature 213. Now, when the relay- 204 is again energized by the restoration of the calling device dial to normal, its operation is ine ective to bring about the operation of the interrupter relay 203. Consequently, the wipers 250 an'd 251 of the minor switch M remain positioned until the selector switch S is operated whereupon the deenergization of the relay 201 brings about the restoration of the minor switch M to normal.

It is to be noted that the third leg of the Wheatstone bridge controlcircuit of the selector switch S is unbalanced so as to initiate the operation of this switch upon the lirst mcfement of the wipers 250 and 251 of the minor switch M which is initiated by the operation of the calling subscribers dial. The above described condition wherein the calling device dial returns to normal before the operation of the selector S is an abnormal condition and one that would occurvery seldom in actual practice.,

Returning now to the description of the progress of the connecting it will be recalled that the operation of the relay 403 in the repeater R brought about the connection of direct ground to the release trunk conductor 349. This bringsabout the short circuiting of the ground connection through the relay 304 in the selector switch S. The relay 304 is thereupon deenergized to open a point in its own circuit at armature 330 to open a point in the circuit of the rotary magnet at armature 331 and to complete the control circuit of the repeater R at armature 332.

The restoration of the mino-r switch M in the common equalizing and repeating equipment J to normal, as stated before, removesv the resistance from the fourth leg of the bridge and if the dial is not yet yrestored to normal the operation of the relay 204 responsive to the unbalanced condition is without function since the relay 206 is deenergized to open the circuit of the relay 203.

Now when the calling device dial restores to normal the third andfourth legs of the W heatstone bridge are balanced and there is no current flow through the relay 204. This relay is thereupon deenergized to complete a circuit for the lower winding of the relay 206. The relay 206 is operated to attract its armature'234 thereby establishing a circuit for its upper winding which remains short ci'rcuited so long as the original circuit is maintained.

When the calling device is operated in accordanee with the neXt digit the third leg of the bridge is unbalanced with respect to the fourth leg, the relay 204 is energized to open the previously traced circuit for the lower winding of the rel-ay 206 and to prepare a circuit at front contacts for the interrupter relay 203. The relay 206 is energized to open a point in the circuit of its lower winding at armature 233, to prepare a circuit forthe relay 207 at the front contact of this armature and'to complete a circuit for the interrupter relay 203. The interrupter relay 203 is energized to establish a locking circuit for itself and to complete a circuit for the stepping magnet 208. The stepping magnet 208 operates to open the circuit of the relay 203 to advance the wipers 250 and 251 of the minor switch M one step. The relay 203 is deenergized to open the circuit of the motor magnet 208 which is deenergized to complete a circuit for the interrupter relay 203. The relay 203:

and the motor magnet 208 are alternately operated until the switch wipers 250 and 251 are properly positioned,'that is, until these wipers have assumed a position correspondmg to the setting of the calling device dial. At this point the wiper 250 has inserted a' sufficient amount of resistance in the fourth leg of the bridge to balance it and bring about the deenergization of the relay 204. The deenergizationof the relay 204 serves to complete a. circuit for the relay 207 as before and to open the circuit of the interrupter relay 203. The movement of the switch wiper 251 changes the conductance of the third l` of the bridge extending to the repeater R predetermined amount.

`We shall now consider the effect of the operation of the minor switch M in the common repeating equipment on the repeater R. The controlling circuit to the repeater R eX- tends from ground by way of off normal spring 430 and its resting contact, upper winding of relay 403, normally closed springs` controlled by armature 412, trunk conductor 350, bank contact 347, wiper 342, normally closed springs controlled by armature 332, armature 327 and its fro-nt contact, trunk conductor 150, back contact and armature 182, bank contact 171, wiper 166, armature 161 and its front contact, conductor 178, bank contact with which the wiper. 251 is in engagement, said wiper, armature 231 and its front contact, lower winding of the electro polarized relay 202, upperwmding of differential relay 201, conductor 177, front contact and armature 160, wiper 165, bank contact 170, armature 140 and its back contact, trunk conductor 148, front contact and armature 322, wiper 340, bank contact345, trunk conductor 348, normally closed springs controlled by armature 413, and the resistor 440 of the first leg of the Wheatstone bridge to battery. l

lVhen the wiper 251 is operated by `the movement of the minor switch M a certain amount of resistance is inserted into the control circuit which constitutes'the third leg of the bridge and the relay-*402 in the repeater R is energized. When the relayv 403 in the repeater R is energized, asI previously described, there is a controlling circuit completed for the incoming selector `S1L in the distant exchange. The circuit ofthe selector S1 is thev same as the circuit of the selector S previously described, and the relay in the selector S1 similar to the relay 301 in the selector S is energized as soon as there is a bridge completed across the trunk conductors450 and 451.v This bridge may be traced from the trunk conductor 450 normally closed springs controlled by armature 410, upper winding of relay 405, normal bank contact with which the wiper 434 is in engagement. said wiper, front contact and armature `422, lower winding of electropolarized relay 404 to' trunk conductor 451. the off normal spring 430 Ais without function The relay similar to 301 in the selector S1 at the present time..l -The operation of the is operated to prepare the selector switch for `armature -429 and the relay 405 also serve to operation in a manner similar to that deopen a oint in the locking circuit of the scribed with res ect to the selector S.- In lower winding of the relay403.=""The operthe repeater R t e relay 405 isenergized to ation of the armature 427- of the relay 405 prepare a circuit for the interru terrelay opens a point in the circuit of -the release 401. Now, when the control re ay 402 is magnet 407.

energized, there is a circuit completed which The movement-bf the wiper y 434 of the extends from ground by way of armature minor switch M1 introduces a certainamount 419 and its front contactand armature 428, lof resistance in'. the bridge ofthe trunk conarmature 432 and its back contact, relay 401, du'ctors 45Q/rand 451 which alters the conincassa and normally closed springs controlled by ductance off-the thirdl leg of the Wheatstone armature 411 to battery, The relay 401 is bridgecontrolling the operation of the energized over this circuit and operates to selector S14 Th'e amount' of the yalteration establish a locking circuit for itselt at armavin conductance depends upon the amount ture 416 and to com lete a circuit at armature necessary 1to bring, about the operation of 417 which extends iiom ground upon release the selector S1 to thei-p'roperI position, and trunk conductor 349 by way of armature alsothe proper positioning 01E-fthe other 414 and its back contact, armature 417 and its ysvvitchiner devices by repeated controlling front contact, and stepping magnet 406 of circuits from the repeater-R. lThat is to say, the minor switch M1 to battery. The stepthe movements of thewiper 434 of the minor ping magnet 406 is energized to open the switch introduce an amount of resistance locking circuit of the relay 401 at armature which will be similar to the amount of re- 432 and to advance the switch wipers 433 and sistance introducedby the common repeating 434 one step into engagement with their first equipment in the distant exchange similar 0H normal or second set ot' bank contacts. to the repeating equipmentJ inthe exchange The movement of the wiper 433 serves to inof the line ot' substation A.

troduce a certain amount of resistance in the circuit of the fourth leg ot the bridge While the same manner as the selector S to position the movement of the wiper 434 introduces a its wipers-vertically opposite the proper level resistance in the previously traced control ofvbank contacts and to thenselect an idle circuit for the selector S1. The relay 401 is trunk in the selected level. When an idle deenergized since its circuit is opened by the trunk line has been selected the operation of operation of the stepping magnet 406 and the rel-aysin the selector S1, similarto the this relay is deenergized to open the circuit relays 303 and 304 in the selectorfS serve to of the stepping magnet. The stepping magmomentarily open the control `circuit-exnet is deenergized to complete a circuit for tending to the repeater Rv.- It will be assumed the relay 401. The alternate operation of that the movement'of the selector S1 under the relay 401 and the stepping magnet 406 the control of the repeater R has been such as continues until the switch wipers 433 and to bring the Wipers 455to 457,-inclusive, into 434 of the minor switch M1 are properlyposiengagement with the bank contacts 458 to tioned in accordance with the position of the 460, inclusive, to which the trunk lines comwipers of the minor switch M in the repeatprising conductors 47 O-to 472, inclusive, are ing equipment J, which in turn are posiconnected,- extending' to theA connector tioned directly from the calling subscribers switch H. dial. When the wipers 433 and 434 of minor When the control circuit is opened the re- Iswitch M1 are moved into this position suflay 405 which is maintained energized over cient resistance hasl been introduced into this circuit in the repeater R is deenergized t-he circuit of the fourth leg of the bridge to to complete a circuit lfor its lower Idifferential balance the bridge .and bring about the de` winding at armature 426, to complete a cirenergization of the control relay 402. This cuit for the release magnet407 at armature relay is deenergized to open the circuit of the 427, -to open. a point in the stepping circuit interrupter relay 401 and the rotary moveat armature v428, andat armature-42.9 to open ment of the wipers 433 and 434 ceases. Upon the'controlling circult extendin backto the the iirst off normal step of. the switch the olf common repeating equipment through the normal springs 430 and 431 are shifted. upper Winding o The operation of the off normal spring 431 the relay 403 is-notdeenergized because the serves to prepare a circuit for `the lower lockingv circuit is simultaneouslycompleted winding of the relay 405 while the operation for its lower Winding atthe. normally closed of the off normal spring 430 opens a point in springs controlled by armature 429.

the circuit of the lower winding of the relay The operation ofthe release magnet 407 i 403. However, since the relay 405 is oper- 'brings about the release of the wipers 433 atedv the armature 429 is inengagement with and 434 so Ithat the balancing and. repeating its front contact soA that the shifting of circuits on the repeater Rare-restored to nor- The selector S1 is-thereuponI operated in the relay l403. However,

mal in onder that they ma be operated in accordance with the next 'git.

v In the common line equalizin and repeating equipment J the opening o the controlling circuit extending to the repeater R brings about the deenergization of the relay 201, which is included 1n this circuit. This rela is deenergized to complete a circuit for its ifferential winding on armature 236 to open a -circuit of the relay 206 on armature 237 and to com lete a circuit for the release /magnet 209 at t e back contact of this armature. The release magnet 209 operates to restore the wipers 250 and 251 of the minor sWitclrMy to their normal position. This o eration serves to bring the wipers in position so that they ma be o erated in accordance with'the next digit ialed by the calling subscriber." The relay 206 is deenergized to open a oint in the circuit ofthe interrupter relay 3 at armature 235, to open a point in the circuit of the relay 207 on armature 233 and to repare a circuit for its lpwer windn at t e back contact of this armature. When 51e switch wipers 250 and 251 of the minor switch M are restored to normal, the of. normal sprin s 297 and 238 are shifted. The operation o the oil normal spring 297 opens the circuit of the relay 207 an this relay is deenergized to prepare a point in the circuit of the interrupter relay 203 at armature 213. The operation of the oi normal spring 238 serves to open the circuit of the lower winding of the relay 201 so that this relay ma be energized over the control circuit to t e repeater Rr through its upper winding.

The control circuit to the repeater R is reestablished and the wipers 433 and 434 of the minor switch M1 are restored to normal whereb the oit normal springs 430 and 431 are shi ed and the relay 405 energized again. This ener 'zation of the relay 405 occurs as soon as t e relay 501 in the connector H which'has been selected by the operation of the selector S1 is energized to a ply ground to the release trunk conductor 4 1. The relay 501 in the connector switch H is energized over a circuit which extends to battery through an armature similar to the armature 326 in theselector switch S1. The connection of ground to the release trunk conductor 471 by the operation of the armature 520 and the rela 501 brings about the deenergization of a re ay similar to the relay 304 in the selector S1 and the control circuit is established for the third leg of the Wheatstone bridge controlling circuit associated with the connector switch H. This circuit may be traced from ground by way of oi normal spring 552 and its resting contact, lower winding of rela 501, normally closed springs controlled y armature 548, trunk conductor 472,

bank contact 460, wiper 457, through the selector switch S1,"interexchange trunk conin addition to placing ductor 451, lower winding of the electroolarized relay 404, armature v422 and its ront contact, wiper434, normal bank contact with which said wiper is in engagement uppe winding of relay 405, normally close springs controlled by armature 410, inter-exc ange trunk conductor 450, throu h the selector switch S1, wiper 455, Iban contact 458, trunk conductor 470, normally closed sprlngs controlled by armature 541, resistor 511 constituting one leg of the Wheatstone bridge, armature 597 and its back contact to battery. The relay 501 is energized over this circuit and operates to prepare the Wheatstone bridge circuit at armature 598. The resistance 561, which is included in the circuit of the fourth leg of the bridge serves to compensate for the resistance of the control circuit extending back to the re eater. The relay 500 is deenergized until t e repeater R is operated to alter the conductance of the third leg of the bridge. The relay 501 is also operated to prepare a locking circuit for the lower win ing of the relay 507 round upon the release trunk conductor 471.

In the common repeating equipment J the relay 204 is restored to normal when the calling device dial at the calling substation is restored to normal. The deenergization of the relay 204 operates to complete a circuit for the relay 206. This relay is energized to prepare a circuit for its upper winding at armature 234. When the calling device dial is operated in accordance with the next digit the relay 206 is energized, as is the relay 204 to complete a circuit for the interruptor relay 203. The interrupter relay 203 and the stepping agnet 208 operate as before alternately to rin about the positioning of the wipers 250 an 251 of the minor switch M at their proper point in accordance with the digit dialed by the calling subscriber. The positioning of the wiper 250 serves to balance the fourth leg of the bridge thereby bringing about the deenergization of the relay 204 and stopping the rotation of the switch wiper.. The deenergization of the relay 204 also completes a circuit for the relay '207. The positioning of the wiper 251 brings about the insertion of a certain amount of resistance into the control circuit extending to the repeater R. This brings about energization of the relay 402 in the repeater which is energized to complete a circuit for the interrupter relay 401. The interrupter relay 401 serves to operate the stepping magnet 406 until the wipers 433 and 434 of the minor switch M1 are properly positioned in accordance with the setting of the wipers of the minor switch M in the common repeating equipment. The movement of the switch wiper 433 serves to introduce an amount of resistance in the fourth le of the bridge suiiicient 'to balance the bri ge and to bring about the deenergization of the relay 402 which causes the cessation of the movement of the switch wipers 433 and 434. The movement of the switch wiper 434 introduces a certain amount'of resistance in bridge of the trunk conductors 450 and 451 thereby altering the conductance of the control circuit which constitutes the third leg of the bridge in the repeater B extending to the armature H.

The relay 500 in the connector H is thereupon energized to complete a circuit at armature 516 that extends from ground by Way of said armature and its front contact, back contact and armature 532, and relay 506 to battery. The rela 506 is energized to open a point in the loc ring circuit of the upper winding of the relay 501 at armature 540, to connect ground to the lower winding of relay 501 in multiple with the ground connected to its lower winding through the off normal spring 552, to complete a circuit for itself exclusive ofthe armature 532 of the relay 504 on armature 539, to prepare a circuit for the rotary magnet at armature 538 and to prepare a testing circuit at armature 537. Another result from the operation of the relay 500 is that at armature 515 there is a circuit complete which extends from ground by way of said armature and its front contact, back contact and armature 546, back contact and armature 529, and relay 503 to battery. The relay 503 is energized to establish a locking circuit for itselt1 at armature 527, and to complete a circuit at armature 528 over a path which extends from ground by way of armature 528 and its front contact, armature 525 and its back contact, and vertical magnet 509 to battery. The vertical magnet 509 is energized to raise the switch shaft carryingy the wipers 555 to 558, inclusive, and 560 one step. Another result of the operation of the Vertical magnet 509 is that at armature 529 the circuit of the interrupter relay 503 is opened and this relay is deenergized to open the circuit of the vertical magnet, which also deenergizes. The deenergization of the vertical magnet serves to complete another circuit for the relay 503. The movement of the vertical wipers 560 into engagement with the Vertical bank contact opposite the first-level serves to introduce a certain amount of resistance into the circuit including the fourth leg of the bridge. If the digit 1 has been called by the calling subscriber at sub-station A this movement of the vertical wiper will serve to bring about a balance of the bridge. However, if some other digit than 1 has been dialed the interrupter relay 503 and the vertical magnet 509 are alternately operated until the-switch wipers are brought opposite the proper level of bank contacts. By the operation of the vertical wiper 560 sufficient resistance has been ir.- serted in the fourth leg of the bridge to baltime because the relay 506 is energized to 'maintain this fground connection over a path that extends om ground by way of armature 520 and its front contact, normally closed springs controlled by armature 547, normally closed springs controlled by armature 533, front contact and armature 540, to one terminal of the lower winding of the relay It will be recalled that the lower winding ot the relay 501 included in the control circuit yforming the third leg of the Wheatstone bridge' control circuit, is supplied with ground through the armature 540 of the relay 506. Since the relay 506 is deenergized immediately upon the deenergization of the relay 500 the circuit of the relay 501 is opened. Simultaneously there is a locking circuit completed for the upper winding of the relay 501 to maintain it energized at the normally closed springs controlled by armature 540. Another result of the operation of armature 540 is that the circuit of the fourth leg of the bridge is opened by the removal of the ground from wiper 560. l

The opening of the control circuit formed by the third leg of the controlling bridge i'n the connector H brings about the deenergization of the relay 405 inthe repeater R. The relay 405 is deenergized to bring about the restoration of the wipers 433 and 434 of the minor switch M1 to normal, as well as the opening of the Wheatstone bridge control circuit extending back to the common repeating equipment J.

The opening of the control circuit extending to the repeater J brings about the deenergization oi: the relay 201 which operates to release the wipers 250 and 251 of the minor switch M as well as to bring about the deenergization of the relay 206. Vhen the calling device dial D at the calling sub-station A restores to normal a circuit is completed for the relay 206 in the common repeating equipment J. This relay is energized to prepare a circuit for the interrupter relay 203 as soon as the calling device dial is operated in accordance with the next digit.

When the callng device dial is operated in accordance with the next digit of the calling subscribers number the control relay 204 in 

